Fluid catalytic cracking (FCC) is the largest refining process for gasoline production with global capacity of more than 14.2 million b/d. The process converts heavy feedstocks such as vacuum distillates, residues, and deasphalted oil into lighter products, which are rich in olefins and aromatics. FCC catalysts are typically solid acids of fine-particles especially zeolites (synthetic Y-faujasite), aluminum silicate, treated clay (kaolin), bauxite, and silica-alumina. The zeolite content in commercial FCC catalysts is generally in the range of 5-40 wt %, or greater, while the balance is silica-alumina amorphous matrix. Additives to the FCC process amount usually to no more than 10% of the catalyst, and they are basically used to enhance octane, as metal passivators, SOx reducing agents, CO oxidation and, recently, for gasoline sulfur reduction.
Stringent environmental regulations that target the sulfur content of gasoline and tailpipe emissions are being enforced worldwide. Sulfur in gasoline increases SOx emissions in combustion gases, reduces the activity of vehicle catalytic converters, and promotes corrosion of engine parts. The upper limit of sulfur in gasoline in the US and European Union will soon be set at 30 ppm as a refinery average. Moreover, the introduction of “sulfur free fuels” (<10 ppm) has been proposed in many countries for the year 2007. Also, many Asian countries have recently decreased the permitted sulfur specifications in transportation fuels.
A number of options are available for the reduction of sulfur in gasoline. The main options are hydrotreating the FCC feed, hydrotreating product naphtha, lowering the end boiling point of FCC gasoline, and the use of sulfur reducing additive in FCC catalysts. The first two options are highly capital intensive. A disadvantage regarding the third option is that the lowering of end boiling point will also reduce the octane number, in addition to reducing the yield of gasoline. From the economic point of view, the last option is the most desirable since this will selectively desulfurize the gasoline fraction without the need for additional treatment. It has been reported that sulfur reduction by FCC additives or catalysts offers economic advantages over the standard solution-selective gasoline hydrotreating or HDS methods. (Lesemann and Schult [2003]).
Various catalytic materials for effecting a sulfur reduction have been developed for use during the FCC process. The sulfur reduction component may be a separate additive to the FCC catalyst or part of a FCC sulfur reduction catalyst. However, the levels of sulfur in gasoline are still not low enough and, accordingly, are unacceptable.
A catalyst additive for the reduction of sulfur in FCC gasoline cracking products was proposed by Wormbecher in U.S. Pat. No. 5,376,608, which is incorporated herein by reference, and Kim in U.S. Pat. No. 5,525,210, which is incorporated herein by reference, using a cracking catalyst additive of an alumina-supported Lewis acid for the production of reduced-sulfur gasoline. It was also disclosed that the Lewis acid may comprise components and compounds including Zn, Cu, Ni, Ag, Cd and Ga deposited on aluminum oxide. However, this system has not achieved significant commercial success.
Another composition disclosed in U.S. Pat. No. 6,036,847 by Ziebarth, which is incorporated herein by reference, et al. used 10 wt % of a composition containing Zn supported on alumina and titania as an additive in the cracking of 2.7 wt % sulfur vacuum gas oil (VGO) feed. The results indicated that the combination of alumina-supported Lewis acid component and titania-containing component resulted in greater sulfur reduction than the use of either component alone.
Another additive, disclosed by Myrstad et al. in U.S. Pat. No. 6,497,811, which is incorporated herein by reference, comprised a composition of a hydrotalcite material, which had been impregnated with a Lewis acid, and optionally an FCC-catalyst. The Lewis acid was selected from the group comprising elements and compounds of the transition metals, and preferably Zn, Cu, Ni, Co, Fe and Mn, most preferably Zn.
Another additive disclosed by Roberie et al. in U.S. Pat. No. 6,482,315, which is incorporated herein by reference, used a composition comprising vanadium supported on a refractory inorganic oxide selected from the group consisting of alumina, silica, clay and mixtures thereof. When using 2 wt. % vanadium-containing additive, a 33% reduction in gasoline sulfur was achieved.
Various papers, published by Andersson, P. et al., Catalysis Today 53:565 (1991), Beltran F. et al, Applied Catalysis Environmental 34:137 (2001) and 42: 145 (2003), relate in only a very general manner to the concept of the present invention.